Use new FailedWithMessage matcher in DWARFDebugLineTest.cpp

Summary:
This should produce slightly better error messages in case of failures.
Only slightly, because this code was pretty careful about that to begin
with -- I've seen code which does much worse.

Reviewers: jhenderson, dblaikie

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D74899